Solved Day 7 of AOC2021 in R, fixed a typo in Day 6 comment

akulumbeg · akulumbeg · commit 046539357f30 · 2021-12-07T11:53:20.000+01:00
diff --git a/2021/README.md b/2021/README.md
@@ -8,6 +8,8 @@
 | [Day 4: Giant Squid](https://adventofcode.com/2021/day/4) | [Data](data/day4.txt) | [R - D4](solutionsR/day4.R) |   | ⭐ | ⭐ |
 | [Day 5: Hydrothermal Venture](https://adventofcode.com/2021/day/5) | [Data](data/day5.txt) | [R - D5](solutionsR/day5.R) |   | ⭐ | ⭐ |
 | [Day 6: Lanternfish](https://adventofcode.com/2021/day/6) | [Data](data/day6.txt) | [R - D6](solutionsR/day6.R) |   | ⭐ | ⭐ |
+| [Day 7: The Treachery of Whales](https://adventofcode.com/2021/day/7) | [Data](data/day7.txt) | [R - D7](solutionsR/day7.R) |   | ⭐ | ⭐ |
+
 
 ### Notes
 
diff --git a/2021/assignments/day7.md b/2021/assignments/day7.md
@@ -0,0 +1,56 @@
+**--- Day 7: The Treachery of Whales ---**
+
+A giant whale has decided your submarine is its next meal, and it's much faster than you are. There's nowhere to run!
+
+Suddenly, a swarm of crabs (each in its own tiny submarine - it's too deep for them otherwise) zooms in to rescue you! They seem to be preparing to blast a hole in the ocean floor; sensors indicate a massive underground cave system just beyond where they're aiming!
+
+The crab submarines all need to be aligned before they'll have enough power to blast a large enough hole for your submarine to get through. However, it doesn't look like they'll be aligned before the whale catches you! Maybe you can help?
+
+There's one major catch - crab submarines can only move horizontally.
+
+You quickly make a list of the horizontal position of each crab (your puzzle input). Crab submarines have limited fuel, so you need to find a way to make all of their horizontal positions match while requiring them to spend as little fuel as possible.
+
+For example, consider the following horizontal positions:
+
+16,1,2,0,4,2,7,1,2,14
+This means there's a crab with horizontal position 16, a crab with horizontal position 1, and so on.
+
+Each change of 1 step in horizontal position of a single crab costs 1 fuel. You could choose any horizontal position to align them all on, but the one that costs the least fuel is horizontal position 2:
+
+    Move from 16 to 2: 14 fuel
+    Move from 1 to 2: 1 fuel
+    Move from 2 to 2: 0 fuel
+    Move from 0 to 2: 2 fuel
+    Move from 4 to 2: 2 fuel
+    Move from 2 to 2: 0 fuel
+    Move from 7 to 2: 5 fuel
+    Move from 1 to 2: 1 fuel
+    Move from 2 to 2: 0 fuel
+    Move from 14 to 2: 12 fuel
+
+This costs a total of 37 fuel. This is the cheapest possible outcome; more expensive outcomes include aligning at position 1 (41 fuel), position 3 (39 fuel), or position 10 (71 fuel).
+
+Determine the horizontal position that the crabs can align to using the least fuel possible. **How much fuel must they spend to align to that position?**
+
+**--- Part Two ---**
+
+The crabs don't seem interested in your proposed solution. Perhaps you misunderstand crab engineering?
+
+As it turns out, crab submarine engines don't burn fuel at a constant rate. Instead, each change of 1 step in horizontal position costs 1 more unit of fuel than the last: the first step costs 1, the second step costs 2, the third step costs 3, and so on.
+
+As each crab moves, moving further becomes more expensive. This changes the best horizontal position to align them all on; in the example above, this becomes 5:
+
+    Move from 16 to 5: 66 fuel
+    Move from 1 to 5: 10 fuel
+    Move from 2 to 5: 6 fuel
+    Move from 0 to 5: 15 fuel
+    Move from 4 to 5: 1 fuel
+    Move from 2 to 5: 6 fuel
+    Move from 7 to 5: 3 fuel
+    Move from 1 to 5: 10 fuel
+    Move from 2 to 5: 6 fuel
+    Move from 14 to 5: 45 fuel
+
+This costs a total of 168 fuel. This is the new cheapest possible outcome; the old alignment position (2) now costs 206 fuel instead.
+
+Determine the horizontal position that the crabs can align to using the least fuel possible so they can make you an escape route! **How much fuel must they spend to align to that position?**
diff --git a/2021/data/day7.txt b/2021/data/day7.txt
@@ -0,0 +1 @@
+1101,1,29,67,1102,0,1,65,1008,65,35,66,1005,66,28,1,67,65,20,4,0,1001,65,1,65,1106,0,8,99,35,67,101,99,105,32,110,39,101,115,116,32,112,97,115,32,117,110,101,32,105,110,116,99,111,100,101,32,112,114,111,103,114,97,109,10,52,1088,462,1398,576,241,636,512,28,390,168,262,6,489,1152,466,539,133,159,1481,128,198,858,57,12,1155,400,137,557,1370,440,885,1433,360,387,5,173,397,465,426,365,470,456,45,1052,1116,26,17,585,647,357,786,313,1124,346,694,941,124,825,243,852,76,618,436,596,14,958,969,895,1745,246,822,239,952,928,206,406,190,459,841,25,1087,299,962,15,1539,1003,456,51,546,858,137,1214,110,936,975,1164,51,82,947,1354,312,132,261,181,287,107,1411,332,930,60,1458,22,248,175,3,946,1097,35,231,648,109,313,1061,163,1382,80,912,89,718,1068,419,703,155,321,909,9,212,478,315,118,206,38,125,130,1391,229,8,44,571,432,24,283,0,941,422,251,686,578,154,123,489,86,1217,129,227,638,47,187,946,2,536,227,640,1170,1444,286,1280,83,1253,1735,70,52,104,658,367,302,462,394,13,798,514,104,260,479,526,632,1161,1118,320,196,262,571,1319,594,131,797,37,566,1054,271,159,1021,244,204,447,624,825,723,364,234,105,362,305,391,681,692,89,380,104,1217,814,1467,898,207,1345,94,10,1380,50,1192,178,1539,1712,145,390,9,878,144,1241,395,10,41,80,1719,1077,113,46,1699,130,91,723,359,1617,1065,530,1058,903,163,412,45,858,10,1704,141,451,1314,879,13,857,905,87,830,1228,25,1594,153,4,585,46,862,265,833,301,473,458,85,254,22,266,543,32,939,1113,228,544,205,1617,1109,445,86,5,278,16,784,303,1022,1014,162,714,447,656,834,138,448,30,85,371,951,1256,842,5,460,919,1019,785,1275,616,1593,168,1727,311,950,1299,1131,796,522,443,703,836,47,300,449,11,360,682,487,108,1396,623,1108,239,379,0,822,109,60,98,667,242,1398,650,25,376,168,46,259,138,254,1631,953,776,166,0,628,75,413,1401,69,462,883,877,96,314,825,346,932,352,1086,143,507,134,557,31,1663,565,275,207,330,702,53,1085,259,14,26,851,1571,1829,1513,356,70,1393,426,345,412,129,908,959,896,1578,617,428,222,1256,3,863,237,5,357,92,292,514,4,919,5,848,1605,149,959,376,1709,410,460,646,389,13,1388,294,1151,652,10,113,769,1519,57,685,1132,1,417,1369,1396,248,496,145,64,798,719,716,845,168,1,147,347,239,512,19,478,336,20,327,487,141,37,96,331,826,1347,479,182,601,233,564,196,0,811,19,318,86,1442,468,396,298,46,661,339,914,54,560,91,284,829,1710,478,318,780,738,807,1017,166,48,358,193,466,831,138,226,5,24,251,119,644,545,588,170,890,248,596,310,612,479,366,1374,465,32,467,79,603,220,1138,168,968,420,129,90,214,652,408,169,0,173,19,312,65,38,115,325,158,1458,744,1529,361,360,77,75,130,111,175,34,676,169,384,473,296,701,84,11,1862,223,193,118,678,403,1097,2,1318,190,590,96,47,69,212,520,786,1569,703,1776,140,12,741,906,29,115,30,196,821,23,51,540,225,891,133,907,567,143,44,371,1038,237,0,222,1327,760,854,1,29,14,65,98,25,233,423,63,382,648,257,160,71,1287,315,627,40,159,202,112,657,87,94,93,362,23,501,870,1114,946,1007,453,159,493,590,665,28,435,7,1238,1846,758,174,258,972,557,1431,482,429,57,389,651,1089,1490,821,844,458,712,259,433,418,344,466,60,123,1604,897,1346,198,143,259,49,770,1703,900,1364,450,498,30,543,322,3,533,508,444,148,927,72,321,733,689,24,44,685,1021,324,182,1737,975,387,143,176,478,602,752,203,130,169,165,41,119,35,175,763,1147,5,137,10,357,54,1209,182,298,156,1488,176,86,548,2,37,36,76,100,1369,1174,322,32,573,107,375,1210,51,597,902,878,919,379,125,26,1240,7,7,131,913,994,1097,576,112,694,805,551,512,663,361,747,161,691,63,119,47,89,6,258,57,537,654,757,1202,922,475,347,193,79,1177,443,33,1257,1070,118,810,117,37,226,230,552,618,341,530,681,1015,358,846,276,1149,210,525,1144,272,30,551,55,512,229,90,1144,389,500,372,92,58,598,1362,475,70,748,1217,442,28,334,369,768,169,405,1058,759,1087,268,714,81,594,1423,1004,694,61,1032,895,1321,95,1512,646,818,845,1275,294,883,1684,1062,2,851,304,306,128,1523,1594,190,73,809,175,321,407,424,109,48,234,437,968,284,1069,181,340,149,9,163,863,17,584,421,79,164,913,81
diff --git a/2021/solutionsR/day6.R b/2021/solutionsR/day6.R
@@ -1,4 +1,4 @@
-# Day 6 - Part  ----------------------------------------------------------
+# Day 6 - Part  1 ----------------------------------------------------------
 
 input <- scan("2021/data/day6.txt", sep=",")
 
diff --git a/2021/solutionsR/day7.R b/2021/solutionsR/day7.R
@@ -0,0 +1,24 @@
+# Day 7 - Part 1 ----------------------------------------------------------
+
+input <- scan("2021/data/day7.txt", sep=",")
+
+# median value is implicitly the most optimal
+fuel <- abs(input - median(input))  # take the abs distance of each element 
+                                    # from median
+sum(fuel)                           # add everything up
+
+# Day 7 - Part 2 ----------------------------------------------------------
+
+input <- scan("2021/data/day7.txt", sep=",")
+
+# the formula for the linearly increasing fuel cost
+# can be expressed as n * ((n+1)/2), where n is the distance
+fpd <- function(dist) {
+  dist * (dist + 1) / 2
+}                      
+
+# the most efficient distances is the one closest to the mean
+# the fpd function produces fuel per crab's distance
+fuel <- fpd(abs(floor(mean(input)) - input))
+
+sum(fuel)                           # add everything up
diff --git a/README.md b/README.md
@@ -39,7 +39,7 @@ C++ is a language that I intend to learn without any prior knowledge, therefore,
 
 [**2021**](/2021/)
 
-    R      [======                   ] 6/25
+    R      [=======                  ] 7/25
     Python [                         ] 0/25
 
 [**2020**](/2020/)

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`@@ -0,0 +1 @@`
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Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-# Day 6 - Part ----------------------------------------------------------`
	`1`	`+# Day 6 - Part 1 ----------------------------------------------------------`
`2`	`2`
`3`	`3`	`input <- scan("2021/data/day6.txt", sep=",")`
`4`	`4`